The Australian Transport Safety Bureau (ATSB) is Australia's national transport safety investigator. The ATSB's function is to improve safety and public confidence in the aviation, marine and rail modes of transport. The ATSB is Australia's prime agency for the independent investigation of civil aviation, rail and maritime accidents, incidents and safety deficiencies.

Summary

Summary

On 11 November, 1998, VH-LPI, a Saab 340A turbo-propeller
aircraft was enroute between Albury, NSW and Melbourne, Victoria on
a scheduled public transport service. The aircraft was operating in
instrument meteorological conditions and had accumulated a deposit
of ice on the wings and windscreen wipers. The crew interpreted
this ice deposit as being less than that required for them to
activate the de-ice systems on the wing leading edges, in
accordance with the aircraft flight manual procedures. As the
aircraft approached Melbourne the crew were instructed to enter a
holding pattern at Eildon Weir. The crew acknowledged this
instruction and reduced power in order to slow the aircraft to the
holding pattern airspeed. The crew subsequently allowed the
airspeed to fall below the target speed of 154 knots, and despite
remedial action, did not regain the target speed.

Shortly after the aircraft entered the holding pattern it
suffered an aerodynamic stall and rolled approximately 126 degrees
to the left and pitched nose down to approximately 35 degrees. The
crew regained control after approximately 10 seconds. The aircraft
lost 2,300 ft of altitude. The crew was not provided with a stall
warning prior to the stall.

The investigation found that despite being certified to all
required certification standards at the time, the Saab 340 aircraft
can suffer from an aerodynamic stall whilst operating in icing
conditions without the required warnings being provided to flight
crew. This problem had been highlighted when the aircraft was
introduced to operations in Canada and as a result a modified stall
warning system was mandated for aircraft operated in Canada. This
modification was not fitted to other Saab 340 aircraft
worldwide.

The investigation also found a number of other occurrences
involving Saab 340 aircraft where little or no stall warning had
been provided to the crew while operating in icing conditions.
Deficiencies were found in the operator's manuals, procedures and
training.

During the course of the investigation, a number of
recommendations were made in 1998 and 1999 concerning flight in
icing conditions and modifications to the Saab 340 stall warning
system. The completion of the investigation and finalisation of the
report were the result of extensive consultation with the aircraft
manufacturer and certification authorities.